text: In the presence of a static external electric field the  degeneracy of each rotational state is partly removed, an instance of a Stark effect. For example, in linear molecules each energy level is split into  components. The extent of splitting depends on the square of the electric field strength and the square of the dipole moment of the molecule. In principle this provides a means to determine the value of the molecular dipole moment with high precision. Examples include carbonyl sulfide, OCS, with . However, because the splitting depends on μ, the orientation of the dipole must be deduced from quantum mechanical considerations.
  A similar removal of degeneracy will occur when a paramagnetic molecule is placed in a magnetic field, an instance of the Zeeman effect. Most species which can be observed in the gaseous state are diamagnetic . Exceptions are odd-electron molecules such as nitric oxide, NO, nitrogen dioxide, , some chlorine oxides and the hydroxyl radical. The Zeeman effect has been observed with dioxygen,